Effect of Gluconate Molecules on the Reaction Kinetics of C-(N)-A-S-H and N-A-S-H Gel Formation

Author

Jiafeng Kong
Chao Sun
Zuhua Zhang
Chenglong Cai
Yubin Cao
Yanru Wang
Hongyan Ma, Missouri University of Science and TechnologyFollow
Xuesen Zeng
Hao Wang

Abstract

Organic ligands are widely used to regulate setting in cementitious binders, yet their chemistry-selective action in geopolymers (GPs) remains unclear. Here we isolate the role of sodium gluconate (SG) in early reaction kinetics across a Ca-rich GP that forms a calcium-(sodium)-aluminosilicate hydrate (C-(N)-A-S-H) gel and a Ca-poor GP that forms a sodium-aluminosilicate hydrate (N-A-S-H) gel. Four GPs spanning Ca/Si ≈ 1.01 to 0.01 were prepared with identical activator chemistry and dosages of SG up to 5 wt.% of precursors. Setting time, isothermal calorimetry, pore-solution speciation (TOC, ICP-OES, and pH), selective dissolution (reaction extent), low-field¹H NMR, XRD, FTIR, SEM-EDS, and Avrami analysis were combined. In the Ca-rich GP, SG delayed the main peak of heat flow and setting but increased the cumulated heat in the first 72 h, so increased reaction extent and compressive strength. Mass-balance fits showed strong early Ca²⁺mobilization per mol of gluconate, consistent with Ca-gluconate complexation and ligand-assisted dissolution. Avrami analysis indicated lower exponents but higher apparent growth rates, and FTIR revealed greater silicate cross-linking. In the Ca-poor GP, SG had little to no retardation and sometimes slightly accelerated setting, with negligible changes in reaction extent and compressive strength due to electrolyte-driven aggregation rather than Ca-controlled nucleation. These results indicated that SG acted as a Ca-complexing retarder in the C-(N)-A-S-H-dominated GP but mainly as an inert electrolyte in the N-A-S-H-dominated GP. Therefore, moderate SG can tune induction and improve early gel yield in the Ca-rich GP, whereas benefits in the Ca-poor GP are limited.

Recommended Citation

J. Kong et al., "Effect of Gluconate Molecules on the Reaction Kinetics of C-(N)-A-S-H and N-A-S-H Gel Formation," Journal of Materials Chemistry A, Royal Society of Chemistry, Jan 2025.

The definitive version is available at https://doi.org/10.1039/d5ta07856c

Department(s)

Civil, Architectural and Environmental Engineering

International Standard Serial Number (ISSN)

2050-7496; 2050-7488

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Royal Society of Chemistry, All rights reserved.

Publication Date

01 Jan 2025